Convert cycles closure (shader) output to colors?
No.

Long answer: Closures (the green sockets) are symbolic descriptions of lighting behavior on a surface. They only result in a color value after evaluation of all the possible incoming light directions by the renderer.

Now, when you talk about using the result of an Ambient Occlusion shader for mixing other shaders, this describes a physical or chemical effect which is not part of the basic pathtracer model with inert materials, i.e. the light influences the physical properties of the material (which in turn could change lighting and so on ...).

A good illustrating example is phosphorescence - if you wanted to implement this with cycles you have to bake a map of the "charge" and use that for an emission shader, while also reducing the charge over time as well as increasing it with incoming light. The important point is that this whole physical simulation is outside of the actual pathtracer and only communicates with cycles via image textures (much like dynamic paint).

The key missing feature is baking of course. It will eventually be added to cycles, but for the time being you'll have to resort to using Blender Internal or some external renderer (or just make an image map by hand).